Indexing mechanism

ABSTRACT

An indexing mechanism comprising a body ( 10 ) mounted so as to be rotatble about an axis; means ( 3 ) for rotating said body about said axis; first cam means ( 9, 10 ) for displacing said body along said axis away from an axial rest position during rotation of said body in a first direction; biassing means ( 11 ) for restoring the body to its axial rest position on completion of a rotation or a predetermined portion thereof of the body; means ( 8   a ) for detecting the axial movement of the body when it is being restored to its axial rest position; and second cam means ( 2, 9 ) permitting said body to be rotated in a second direction opposite the first direction.

The present invention relates to indexing mechanisms, in particularsuitable for use in meters (e.g. for measuring the supply of water, gasor electricity) or odometers and other counting devices.

WO 89/05016 discloses a number wheel counter in which a worm gearengages a worm wheel connected to a number wheel. Rotation of the wormgear about its longitudinal axis effects rotation of the worm wheel andthereby rotation of the number wheel. However, a cam means is providedfor displacing the worm gear axially away from a rest position insynchronism with rotation of the worm gear such that the worm wheelremains stationary over a worm gear rotation corresponding to a numberinterval of the number wheel. At the end of a rotation the worm gear israpidly restored to its rest position by means of a lever arrangementincluding a spring so as to drive the number wheel through a numberinterval. As a result, during almost the entire rotation of the wormgear the number wheel remains stationary enabling unambiguous readout,and only at the end of a rotation of the worm gear the readout changes.

Whilst this wheel counter works reliably in many applications it hasbeen appreciated by the present inventor that, whilst in its restposition the worm gear of this known device cannot be rotated inreverse. Merely before completion of a full rotation of the worm gearthis (incomplete) rotational movement can be reversed, but no furtherreverse rotational movement is possible once the worm gear has beenreversed to the rest position. Hence, if the worm gear in this device isforced in the reverse direction the cam means will jam, and the devicewill break.

The present inventor has further appreciated that the arrangementdisclosed in the above publication requires a relatively high inputtorque to overcome the friction between the rotating worm gear and thelever.

The present invention seeks to address these problems. Preferredembodiments of the present invention include an indexing mechanism whichcounts both in forward and reverse directions, and one that counts inthe forward direction, regardless of the rotational direction of theinput. The inventor has further appreciated that the underlyingprinciple of the present invention can also be employed in an indexingmechanism which is read out e.g. electronically.

In one aspect the present invention provides an indexing mechanismcomprising

-   -   a body (10, 10A, 10B, 10C) mounted so as to be rotatable about        an axis;    -   means (3) for rotating said body about said axis;    -   first cam means (9, 9C, 10, 10A, 10B, 10C) for displacing said        body along said axis away from an axial rest position during        rotation of said body in a first direction;    -   biassing means (11) for restoring the body to its axial rest        position on completion of a rotation or a predetermined portion        thereof of the body;    -   means for detecting the axial movement of the body when it is        being restored to its axial rest position; and    -   second cam means (2, 9, 2A, 9B, 2C) permitting said body to be        rotated in a second direction opposite the first direction.

In a second aspect the present invention provides an indexing mechanismcomprising

-   -   a body (10, 10A, 10B, 10C) mounted so as to be rotatable about        an axis;    -   means (3) for rotating said body about said axis;    -   first cam means (9, 9C, 10, 10A, 10B, 10C) for displacing said        body along said axis away from an axial rest position during        rotation of said body in a first direction;    -   a spring (11), preferably a compressive spring, located        coaxially with said body and for restoring the body to its axial        rest position on completion of a rotation or a predetermined        portion thereof of the body;    -   means for detecting the axial movement of the body when it is        being restored to its axial rest position; and    -   means for permitting said body to be rotated in a second        direction opposite the first direction.

In those embodiments in which the axial displacement is detected bymeans other than a wheel the rotational input movement may be translatedinto a “sawtooth” or similar stepwise movement along the axis. As theaxial movement of the body, when it is being restored to its axial restposition, depends on fixed parameters, in particular the module of thebiassing means (e.g. a compressive spring) and not on the inputrotational speed this axial movement towards the rest position can bedetected with higher accuracy than may be possible in arrangements inwhich the input rotational movement is detected directly, especially atlow input rotational speeds.

Preferred features are set out in the dependent claims.

The invention also provides a meter or other counting device comprisingan indexing mechanism as set forth above.

Preferred features of the present invention will now be described, byway of example only, with reference to the accompanying drawings, inwhich:—

FIG. 1 shows an exploded, three-dimensional view of an indexingmechanism according to a first embodiment of the present invention.

FIG. 2 shows a three-dimensional view of the indexing mechanism of thefirst embodiment, partly cut-away.

FIG. 3 shows an exploded, three-dimensional view of some parts of theembodiment shown in FIGS. 1 and 2.

FIG. 4 shows an exploded, three-dimensional view of an indexingmechanism according to a second embodiment of the present invention.

FIG. 5 shows a three-dimensional view of the indexing mechanismaccording to the second embodiment, with the upper bearing plateremoved.

FIG. 6 shows a three-dimensional view of the indexing mechanism shown inFIGS. 4 and 5, partly cut-away.

FIG. 7 shows an exploded, three-dimensional view of some parts of theembodiments shown in FIGS. 4 to 6.

FIG. 8 shows an exploded three-dimensional view of an indexing mechanismaccording to a third embodiment of the present invention.

FIG. 9 shows a three-dimensional view of the indexing mechanism shown inFIG. 8 with the upper bearing plate removed.

FIG. 10 shows a three-dimensional view of the indexing mechanism shownin FIGS. 8 and 9, partly cut-away.

FIG. 11 shows an exploded, three-dimensional view of some parts of theindexing mechanism shown in FIGS. 8 to 10.

FIG. 12 shows an exploded, three-dimensional view of two cam bodiesshown in FIG. 11.

FIG. 13 shows an exploded, three-dimensional view of an indexingmechanism according to a fourth embodiment of the present invention.

FIG. 14 shows a three-dimensional view of some parts of the embodimentshown in FIG. 13, partly cut-away.

FIGS. 15 to 22 show exploded, three-dimensional views of three cambodies shown in FIG. 13; in FIGS. 16, 18 and 21 these are shown partlycut-away.

Referring to FIGS. 1 to 3, a first embodiment of the present inventionwill be described The indexing mechanism of the first embodiment formspart of a water meter and comprises upper and lower bearing plates 2, 5,between which most of the remaining parts of the mechanism are located.A cup and spindle 12 is provided, which carries a first cam body 10 anda compressive spring 11 located between the cup and the first cam body.The cup further holds a bearing spindle insert 13, which is rotatablymounted in a bearing of the lower bearing plate 5. The bearing spindleinsert 13 runs on a jewel 4. The upper end of the spindle furthercarries a second cam body 9 and is received within upper bearing plate2. In the embodiment shown in the drawings the spindle 12 penetrates theupper bearing plate 2. On the upper side of the upper bearing plate thespindle 12 carries a pointer, which rotates with the spindle 12. As canbest be seen in FIG. 1, upper bearing plate 2 is integrally formed witha cam, thus constituting a third cam body.

The indexing mechanism further comprises a drive roller 8, driving aroller 7 on which numbers may be marked to indicate a count. Furtherrollers may be provided on roller bank spindle 6 so as to indicateseveral digits of a count. Formed onto drive roller 8 are a plurality ofpegs 8A via which the drive roller 8 can be driven. A helicoidal cam isformed onto the outer surface of the first cam body 10. This helicoidalcam engages with pegs 8A so as to drive the drive roller 8. The firstcam body 10 can be rotated by means of drive gear 3, which has teethengaging with teeth formed on the first cam body 10. Cam body 10 can bedisplaced axially on spindle 12. The first cam body 10 is biassed bycompressive spring 11, which is located coaxial with the first cam body10, towards a rest position, away from the lower bearing plate 5. Thefirst cam body is further formed with an internal helicoidal cam (bestseen in FIG. 3), which conforms with a cam on that surface of the secondcam body 9 which faces the first cam body 10. On the other side of thesecond cam body 9 there is provided a further helicoidal cam, conformingwith a cam on the lower side of the upper bearing plate 2 (the third cambody). The pitch of the cam formed by opposing surfaces of the secondand third cam body 9 and 2 is much smaller than the pitch of the camformed by opposing surfaces of the first and second cam body 10 and 9,which in turn corresponds to the pitch of the external cam of the firstcam body 10 and also the distance between two pegs 8A of drive roller 8.The sense of the helicoidal cam formed between the second and third cambodies 9 and 2 is opposite that of the cam formed between the first andsecond cam bodies 10 and 9 and the external cam on the first cam body10.

During operation in a forward direction, the first cam body 10 isrotated in a first direction by means of drive gear 3. As the first cambody is rotated, the cam formed between the first and second cam bodies10, 9 displaces the first cam body 10 axially towards the lower bearingplate 5. However, as the pitch of the external cam on the first cam body10 is the same as that of the cam formed between the first and secondcam bodies 10, 9, the external cam remains stationary relative to thedrive roller pegs 8A, and thus does not drive them. When a full rotationof the first cam body is completed the helicoidal cam surfaces formedbetween the first and second cam bodies 10, 9 reach the end ofengagement and the first cam body 10 is forced back up to the restposition without rotation with a rapid snap movement by the compressivespring 11. During this rapid movement the external cam on cam body 10engages and drives one of the roller pegs 8A upwards, therebyincrementing the roller 7 by one index with a rapid snap movement.During rotation of the spindle 12 the pointer 1 also rotates.

In reverse operation, the first cam body 10 is rotated in a second(opposite) direction by means of drive gear 3. During this movement theopposing cam surfaces formed between the first and second cam bodies 10,9 remain engaged. On the other hand, the cam formed between the secondand third cam bodies 9, 2 displaces the first and second cam bodies 10,9 slightly towards the lower bearing plate 5 until, upon completion of afull rotation, the end of engagement is reached at this cam and thefirst cam bodies 10, 9 are forced back towards the rest position byspring 11. As the pitch of the cam formed between the second and thirdcam bodies 9, 2 is insignificant, the first cam body 10 is not displacedby a large amount. During this rotational movement of the first cam body10 in the second direction the external cam on the first cam body 10drives a drive roller peg 8A downward in a continuous movement. A rapidsnap movement as during forward operation does not take place. It willthus be seen that this embodiment enables the first cam body 10 to berotated in both directions, and the indexing mechanism counts in bothdirections.

A second embodiment will now be described with reference to FIGS. 4 to7, in which like details carry like reference symbols as in FIGS. 1 to3. As in the first embodiment, the indexing mechanism comprises an upperand lower bearing plate 2A and 5A, a roller bank spindle 6, a roller 7,a drive roller 8 carrying a plurality of drive roller pegs 8A and adrive gear 3. A cup and spindle 12 carrying a compressive spring 11,first and second cam bodies 10A and 9 and a bearing spindle 13 is alsoprovided, and a jewel 4 facilitating rotation with respect to the lowerbearing plate 5A. The upper bearing plate 2A is again formed with ahelicoidal cam surface of insignificant pitch on its lower side. Theconfiguration and function of the above parts of the second embodimentare the same as in the first embodiment, except that instead of beingformed with an external helicoidal cam, the first cam body 10A is formedwith a peg 111 for engaging the pegs 8A of drive roller 8.

The second embodiment is provided with a further cup and spindle 12A,bearing spindle 13A, compressive spring 11A, first and second cam bodies15 and 14 and jewel 4. The further cup and spindle 12A is arranged inparallel next to cup and spindle 12. Upper bearing plate 2A is formedwith a further helicoidal cam surface thereby constituting a furtherthird cam body. The further first, second and third cam bodies aremirror-images of the first, second and third cam bodies.

Forward operation of the second embodiment is the same as that of thefirst embodiment as regards the sub-assembly carried by spindle 12,except that, of course, no external helicoidal cam is provided on thefirst cam body 10A. During most of the axial displacement of the firstcam body 10A the peg 111 is not engaged with pegs 8A. Only uponcompletion of a rotation of the first cam body 10A the peg 111, whichthen has reached a position between two adjacent pegs 8A moves upwardsin a rapid snap movement, thereby driving the drive roller 8. Duringthis rapid snap movement, the peg 111A carried by the further first cambody 15 is not in contact with any of the pegs 8A. During rotation ofthe first cam body 10A the further first cam body 15 also rotates, inthe embodiment shown in the same direction, and peg 111A passes betweentwo adjacent pegs 8A. The two opposing cam surfaces between the furtherfirst and second cam bodies 15, 14 are in contact and the further firstand second cam bodies 15, 14 are displaced axially only slightly bymeans of the cam formed between the further second and third cam bodies14, 2A.

When the mechanism is operated in reverse, the roles of thesub-assemblies carried by spindles 12 and 12A are reversed, which meansthat it is now the further first and second cam bodies which are axiallydisplaced by the cam formed therebetween, and upon completion of a fullrotation the further peg 111A drives the drive roller 8 by means of oneof the pegs 8A. The opposing cam surfaces formed on first and second cambodies 10A and 9 remain in contact during this reverse movement and aredisplaced axially only slightly by means of the small-pitched cam formedbetween the second and third cam bodies 9, 2A. Thus it can be seen thatthe second embodiment provides for rapid snap indexing movement ofroller 7 in both directions.

A third embodiment of the present invention will now be described withreference to FIGS. 8 to 12, in which like parts carry like referencenumerals as in FIGS. 1 to 7. The constitution of the third embodiment isbasically the same as that of the first embodiment, except that thefirst, second and third cam bodies 10, 9 and 2 of the first embodimentare replaced by first to fourth cam bodies 10B, 9C, 9B and 2, The firstcam body 10B of the third embodiment is the same as the first cam body10A of the second embodiment, that is, it carries a peg 111 but noexternal helicoidal cam. The second cam body 9C has a lower helicoidalcam surface on its lower side like the second cam body 9 of the firstembodiment. However, on its upper side no cam surface is provided.Instead, a pin 100 is provided in axial direction, which is receivedwithin a crescent-shaped groove 110 provided on the lower side of thethird cam body 9B. A helicoidal cam surface is provided on the uppersurface of the third cam body 9B, having the same pitch as thehelicoidal cam surface formed on the lower surface of the second cambody 9C, but running in opposite direction. The upper bearing plate 2,forming the fourth cam body is provided with a helicoidal cam surfaceconforming with the helicoidal cam surface provided on the upper side ofthe third cam body 9B.

The second and third cam bodies 9C and 9B can be rotated with respect toeach other. However, this movement is limited by movement of pin 100within groove 110. During forward operation the first cam body 10B isrotated by drive gear 3 in a first direction. This drives the second cambody 9C until pin 100 arrives at a stop at one of the ends of groove 110in the third cam body 10B. Once pin 100 has arrived at its stop ingroove 110 it cannot move the third cam body 9 since the cam formedbetween the third and forth cam bodies 9B and 2 would not permit suchmovement. Instead, the first cam body 10B is displaced axially towardsthe lower bearing plate 5, due to the cam formed between the first andsecond cam bodies 10B and 9C. During this movement the peg 111 does notengage any of the pegs 8A. When a full rotation of the first cam body10B with respect to the second cam body 9C has been completed theopposing cam surfaces formed therebetween reach the end of engagement,and the first cam body 10B returns to its rest position with a rapidsnap movement. The peg 111 is formed at such a position on the first cambody 10B that, during this rapid snap movement, it engages one of thedrive pegs 8A to drive the drive roller 8 and the roller 7.

If the sense of rotation of the drive gear 3 is reversed at this stagethe first and second cam bodies 10B and 9C remain engaged and the secondcam body 9C is rotated with respect to the third cam body 9B. Again,this movement is limited by the length of groove 110, and when pin 100has reached a stop at the other end of groove 110 it starts moving thethird cam body 9B with respect to the forth cam body 2. The cam formedbetween the third and forth cam bodies 9B and 2 causes the first tothird cam bodies 10B, 9C and 9B to be displaced axially towards thelower bearing plate 5 until the cam surfaces between the third and forthcam bodies 9B and 2 reach the end of their engagement. During thismovement the peg 111 does not engage any of the drive roller pegs 8A.Only upon completion of a full rotation the first to third cam bodies10B, 9C and 9B return to their rest positions with a rapid snapmovement, and peg 111 drives a drive roller peg 8A with a rapid snapindexing movement.

Whilst during forward operation the peg 111 engages a drive roller peg8A on one side of the drive roller 8 so as to drive the drive roller 8in a first sense, during reverse operation after rotational movement ofthe second cam body 9C with respect to the third cam body 9B defined bythe appropriately chosen length of groove 110 the peg 111 has arrived onthe other side of drive roller 8 for driving a peg 8A on that other sideas to drive the drive roller 8 in the opposite sense.

It can thus be seen be seen that this embodiment enables rapid snapindexing movement of the drive roller 8 in both directions withoutrequiring two sub-assemblies carried by two spindles as in the secondembodiment.

A fourth embodiment is illustrated in FIGS. 13 to 22, in which likeparts carry like reference numerals as in FIGS. 1 to 12. The fourthembodiment is essentially a refinement of the third embodiment.

The main difference between the third and fourth embodiments lies in theshape of the first cam body, 10C in the fourth embodiment. As can bestbe seen in FIG. 14, the first cam body 10C is at least partiallyreceived within the space defined between pegs 8A on drive roller 8,which pegs are, in order to improve mechanical stability and durability,formed with an oblong cross section. Generally speaking the first cambody 10C is formed such that it prevents the drive roller 8 fromrotating except when the drive roller 8 is being driven by the rapidsnap movement of the first cam body 10C. There is hence no danger ofdrive roller 8 being pivoted or rotated accidentally, e.g. due to suddenmovements of the indexing mechanism, tampering or other externalinfluences.

As part of the particular shape of the first cam body 10C which preventsaccidental movement of drive roller 8 the first cam body is formed withtwo pairs of blades 10D (best seen in FIG. 17). Depending on therotational position of the first cam body 10C the blades 10D perform thefunction of driving the drive roller 8 via pegs 8A or of preventing thedrive roller 8 from rotating. During rotation of the first cam body 10Cand axial movement thereof different portions of the first cam body 10Ctake over the function of preventing the drive roller 8 from rotating.

The first cam body 10C of the embodiment illustrated in FIGS. 13-22 isin particular formed with a generally cylindrical central portion 29between two generally cylindric portions 25 and 26 of slightly smallerdiameter (FIGS. 15, 17 and 18). The blades 10D are carried by thecentral cylindrical portion 29. Cylindrical portion 25 is formed withone axially protruding lip 24 and a cut-out portion 28 situateddiametrically opposite the axial lip 24. Similarly, the cylindricalportion 26 has a cut-out portion 27 at the same angular position at thecut-out portion 28. The blades 10D are not all identical. Blades 20 and21, which are situated at the same angular position as the axial lip 24are longer in the circumferential direction than blades 22 and 23, whichare located at the same angular position as cut-out portions 27 and 28.

The spacing in the axial direction between blades 20 and 21 on the onehand and blades 22 and 23 on the other corresponds to the thickness ofthe pegs 8A, so as to enable a said peg 8A to pass between these bladesduring rotation of the first cam body 10C. Similarly the overall axialextent of the pair of blades 20 and 21 and the pair of blades 22 and 23corresponds to the spacing between two adjacent pegs 8A so as to enablethe pairs of blades to pass between two adjacent pegs 8A during anotherpart of the rotation of the first cam body 10C.

During almost the entire rotation of the first cam body 10C the driveroller 8 is prevented from rotating since, depending on the rotationalposition of the first cam body 10C, different ones of the pegs 8A arerestricted in their movement. This movement is in particular restrictedby the steps formed by the three cylindrical portions 25, 26 and 29, theaxial lip 24 and blades 20, 21,22 and 23. Similarly, the cut-outportions 27 and 28 ensure that the first cam body 10C can rotate andmove axially without being restricted by the drive roller 8 or pegs 8A.It can thus be-seen that the particular shape of the first cam body 10Censures that the index mechanism does not jam, whilst preventing thedrive roller 8 from rotating except when it is being indexed by thefirst cam body 10C being restored to its axial rest position.

As a fifth embodiment (a modification of the fourth embodiment), it ispossible to assemble the indexing mechanism such that the axis carryingthe first cam body 10C does not pass through the axis about which thedrive roller 8 rotates, but is offset relative thereto. To this end thecam body axis is located approximately on a tangent to the pitch circleof the centres of the pegs 8A. With this arrangement the first cam body10C only drives the pegs 8A on one side of the drive roller 8,irrespective of the direction of rotation of the first cam body. As aresult the drive roller 8 is driven only in one sense, irrespective ofthe rotational direction of drive gear 3. This can be particularlyuseful if the indexing mechanism is used in an electricity, gas or watermeter since fraudulent attempts to reverse the counter by e.g. reversingelectrical contacts for rotating the drive gear 3 would fail.

The first embodiment can be modified to form a sixth embodiment. To thisend the external helicoidal cam carried by the first cam body 10 isreplaced by two, three or even four helicoidal cams angularlydistributed about the perimeter of the first cam body 10. The cam formedbetween the first and second cam bodies 10, 9 would have to be formedcorrespondingly. More than about 4 cams should, however, not be formedsince this would result in too much friction between the first andsecond cam bodies 10, 9 (as is the case in a ratchet).

In an arrangement with n helicoidal cams arranged on the first cam body10, upon one full rotation of the first cam body the roller 7 is drivennot only through one number interval but through n number intervals.Corresponding modifications are possible with Embodiments 2 and 3, withtwo or more pegs 111 or 111A distributed about the perimeter of thefirst cam body.

All of the above embodiments can be modified to form a seventhembodiment. In the seventh embodiment no roller bank and drive roller 8are required. Further, the first cam body does not require an engagementformation as it is not used to drive a drive gear mechanically. In theseventh embodiment the rapid snap movement of the first cam body is not“detected” mechanically by a drive roller, but electrically, for exampleby means of a reed switch. Processing circuitry may be provided whichensures that the reed switch only detects the rapid snap movement of thefirst cam body when the first cam body is being restored to its axialrest position, but not the axial displacement away from its restposition.

It will be appreciated that the rapid snap movement of the first cambody can also be detected by other means, e.g. optically.

It will also be appreciated that, whilst it is preferred to use acompressive spring for restoring the first cam body to its axial restposition, other forms of springs such as a tension spring may also beused.

While the present invention has been described in its preferredembodiments, it is to be understood that the words which have been usedare words of description rather than limitation and that changes may bemade to the invention without departing from its scope as defined by theappended claims.

Each feature-disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently of other disclosed and/or illustrated features.

Reference numerals used in the claims are for illustration purposesonly, and are not to be understood in a limiting sense.

1. An indexing mechanism comprising: a body (10, 10A, 10B, 10C) mountedso as to be rotatable about an axis; a drive (3) for rotating said bodyabout said axis; a first cam (9, 9C, 10, 10A, 10B, 10C) for displacingsaid body along said axis away from an axial rest position of said bodyduring rotation of said body in a first direction; a biasing device (11)for restoring the body to the axial rest position on completion of arotation or a predetermined portion thereof of the body; a detector fordetecting the axial movement of the body when the body is being restoredto the axial rest position, and for effecting indexing in response tosaid axial movement; and a second cam (2, 9, 2A, 9B, 2C) permitting saidbody to be rotated in a second direction opposite the first direction.2. An indexing mechanism according to claim 1, wherein the second cam isarranged to displace said body along said axis away from the axial restposition during rotation of said body in the second direction.
 3. Anindexing mechanism according to claim 1, wherein the biasing device (11)comprises a spring, preferably a compressive spring, located co-axiallywith said body.
 4. An indexing mechanism according to claim 1, whereinthe second cam (2, 9, 2A) displaces said body axially to a lesser extentthan the first cam (9, 10, 10A).
 5. An indexing mechanism according toclaim 1, wherein the second cam (2, 9B) displaces said body axially tothe same extent as the first cam (10B, 9C).
 6. An indexing mechanismaccording to claim 1, wherein the or each cam comprises a pair ofconforming cam surfaces.
 7. An indexing mechanism according to claim 1,wherein the or each cam comprises at least one helicoidal cam surface(10).
 8. A meter or other counting device comprising an indexingmechanism as claimed in claim
 1. 9. An indexing mechanism comprising: abody (10, 10A, 10B, 10C) mounted so as to be rotatable about an axis; adrive (3) for rotating said body about said axis; a first cam (9, 9C,10, 10A, 10B, 10C) for displacing said body along said axis away from anaxial rest position of said body during rotation of said body in a firstdirection; a spring (11), preferably a compressive spring, locatedcoaxially with said body and for restoring the body to the axial restposition on completion of a rotation or a predetermined portion thereofof the body; a detector for detecting the axial movement of the bodywhen the body is being restored to the axial rest position, and foreffecting indexing in response to said axial movement; and a device (2,9, 2A, 9B, 2C) for permitting said body to be rotated in a seconddirection opposite the first direction.
 10. An indexing mechanismaccording to claim 9, wherein the permitting device (2, 9, 2A) permitssaid body to be rotated in the second direction substantially withoutaxial movement thereof.
 11. An indexing mechanism according to claim 9,wherein the permitting device comprises a second cam.
 12. An indexingmechanism comprising: a body (10, 10A, 10B, 10C) mounted so as to berotatable about an axis; a drive (3) for rotating said body about saidaxis; a first cam (9, 9C, 10, 10A, 10B, 10C) for displacing said bodyalong said axis away from an axial rest position of said body duringrotation of said body in a first direction; a biasing device (11) forrestoring the body to the axial rest position on completion of arotation or a predetermined portion thereof of the body; a detector fordetecting the axial movement of the body when the body is being restoredto the axial rest position, the detector comprising at least one wheel(8) which is indicative of a count; a plurality of first engagementformations (8A) connected to the wheel (8) and in angularly spacedrelationship with each other, wherein the wheel (8) can be driven viathe first engagement formations (8A); wherein said body (10, 10A, 10B,10C) has at least one second engagement formation (10, 10D, 111), forengaging and driving the first engagement formations (8A); wherein thefirst cam (9, 9C, 10, 10A, 10B, 10C) is arranged to displace said bodyalong said axis away from the axial rest position is synchronism withrotation thereof in the first direction, such that the first engagementformations(8A) are not driven by the at least one second engagementformation (10, 111) over a substantial portion of a rotation of saidbody about said axis in the first direction; and wherein, when said bodyis being restored to the axial rest position, the at least one secondengagement formation (10, 10D, 111) drives the plurality of firstengagement formations (8A) so as to index the wheel (8) incrementally ina first sense.
 13. An indexing mechanism according to claim 12, whereina said body (10, 10C) is formed such that the plurality of firstengagement formations is prevented from rotating except when the body isbeing driven by the at least one second engagement formation.
 14. Anindexing mechanism according to claim 12, wherein the first cam body 10Cis shaped such that, during the rotation and axial movement of the firstcam body, different portions thereof prevent the plurality of firstengagement formations (8A) from rotating.
 15. An indexing mechanismaccording to claim 12, wherein the at least one second engagementformation comprises a protrusion or a plurality of axially spacedprotrusions having an overall extent in the axial directioncorresponding to the distance between two adjacent first engagementformations.
 16. An indexing mechanism according to claim 12, wherein theat least one second engagement formation comprises a pair of axiallyspaced protrusions, the axial spacing between the protrusionscorresponding to the thickness of a said first engagement formation. 17.An indexing mechanism according to claim 12, wherein said pair ofprotrusions have an overall extent in the axial direction correspondingto the distance between two adjacent first engagement formations.
 18. Anindexing mechanism according to claim 12, wherein the indexing mechanismfurther comprises at least one third engagement formation (111A) mountedso as to be rotatable about a further axis; a further drive (3, 15) forrotating the at least one third engagement formation (111A) about thefurther axis; and a further cam (15, 14) for displacing the at least onethird engagement formation (111A) along the further axis away from afurther axial rest position in synchronism with rotation thereof in athird direction such that the first engagement formations (8A) remainstationary over a substantial portion of a rotation of the at least onethird engagement formation (111A) about the further axis in the thirddirection; a further biasing device (11A) for restoring the at least onethird engagement formation (111A) to the further axial rest position todrive the plurality of first engagement formations (8A) so as to indexthe wheel (8) incrementally in a second sense opposite the first sense;and a further device (2A, 14) permitting the at least one thirdengagement formation (111A) to be rotated in a fourth direction oppositethe third direction.
 19. An indexing mechanism according to claim 18,wherein the drive and the further drive comprises respective first (10A)and second (15) gears provided with teeth that extend a sufficientdistance along said axis and the further axis, to remain continuously incontact with teeth of one and the same drive gear (3).
 20. An indexingmechanism according to claim 19, wherein the further permitting devicecomprises a second further cam.
 21. An indexing mechanism according toclaim 18, wherein the further biasing device comprises a further spring,preferably a compressive spring.
 22. An indexing mechanism according toclaim 12, comprising a second cam (2, 9, 2A, 9B, 2C) permitting saidbody to be rotated in a second direction opposite the first direction.23. An indexing mechanism according to claim 22 wherein the first camand the second cam are formed by at least three cam bodies (2, 9, 10,2A, 1A), said body constituting a first said cam body, the at least onesecond engagement formation being mounted on said first cam body (10,10A), wherein the first cam (9, 10, 10A) limits rotational movement ofthe first cam body (10, 10A) with respect to the second cam body (9) inthe second direction, and wherein the second cam (2, 9, 2A) limitsrotational movement of the second cam body (9) with respect to the thirdcam body (2, 2A) in the first direction.
 24. An indexing mechanismaccording to claim 22, wherein the first cam and the second cam areformed by four cam bodies (2, 2C, 9B, 9C, 10B, 10C), said bodyconstituting a first said cam body, the at least one second engagementformation (111, 10D) being mounted on said first cam body (10B, 10C),wherein the first cam (10B, 10C, 9C) limits rotational movement of thefirst cam body (10B, 10C) with respect to the second cam body (9C) inthe second direction, and the second cam (2, 9B) limits rotationalmovement of the third cam body (9B) with respect to the fourth cam body(2, 2C) in the first direction, wherein there is further provided device(100, 110) for limiting rotational movement of the second cam body (9C)with respect to the third cam body (9B) in either direction.
 25. Anindexing mechanism according to claim 24, wherein the rotation-limitingdevice (100, 110) permits rotational movement of the second cam body(9C) with respect to the third cam body (9B) without axial movement ofsaid body.
 26. An indexing mechanism according to claim 25, wherein therotation limiting device (100, 110) limits rotational movement of thesecond cam body (9C) with respect to the third cam body (9B) such as topermit movement of the at least one second engagement formation (111,10D) from a first position for driving the wheel (8) in the first senseto a second position for driving the wheel (8) in a second senseopposite the first sense.
 27. An indexing mechanism according to claim24, wherein the rotation limiting device (100, 110) limits rotationalmovement of the second cam body (9C) with respect to the third cam body(9B) such as to permit movement of the at least one second engagementformation (111, 10D) from a first position for driving the wheel (8) inthe first sense to a second position for driving the wheel (8) in asecond sense opposite the first sense.
 28. An indexing mechanismaccording to claim 22, wherein the at least one second engagementformation drives the wheel in the first sense regardless of whether saidbody is rotated in the first direction or the second direction.